1. Field of the Invention
The invention relates to magnetic cores having a sheared hysteresis loop and somewhat more particularly to magnetic cores comprised of a low-retentivity amorphous alloy.
2. Prior Art
Electromagnetic elements comprised of magnetic cores formed of low-retentivity amorphous alloys are known, for example see German Offenlegungsschrift No. 25 46 676 and 25 53 003.
As is known, amorphous metal alloys can be manufactured by cooling a suitable melt so quickly that a solidification without crystallization occurs. In this manner, precisely during formation, alloy bodies can be produced in the form of relatively thin bands or strips having a thickness of, for example, a few hundredths of a millimeter and a width which can range from a few millimeters through several centimeters.
Amorphous alloys can be distinguished from crystalline alloys, for example, by means of X-ray diffraction analysis. In contrast to crystalline materials which exhibit characteristically sharp diffraction lines, amorphous metal alloys exhibit broad peaks, the intensity of which change only slowly with the diffraction angle, similar to that of liquids or common glass.
Depending upon the manufacturing conditions, an amorphous alloy can be completely amorphous or comprise a two-phase mixture of amorphous and crystalline states. In general, an amorphous metal alloy is understood in the art as comprising an alloy which is at least 50% amorphous and more preferably at least 80% amorphous.
Each amorphous metal alloy has a characteristic temperature, a so-called crystallization temperature. If one heats an amorphous alloy to or above this characteristic temperature, then the alloy changes into a crystalline state, in which it remains after cooling. However, with heat treatments below the crystallization temperature, the amorphous state is retained.
Heretofore known amorphous metal alloys have the composition M.sub.y X.sub.1-y wherein M represents at least one of the metals selected from the groups consisting of iron, cobalt and nickel and X represents at least one of the so-called glass-forming elements selected from the group consisting of boron, carbon silicon and phosphorous and y is a numeral ranging between approximately 0.60 and 0.95. In addition to the above-enumerated metals M, known amorphous alloys can also contain further metals, such as titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, palladium, platinum, copper, silver and/or gold. Further, the elements aluminum, gallium, indium germanium, tin, arsenic, antimony, bismuth and/or beryllium can also be present in addition to the above-enumerated glass-forming elements X or, under certain conditions, in place thereof.
Amorphous low-retentivity alloys are particularly suited for manufacture of magnetic cores since, as mentioned above, they can be produced directly in the form of thin bands without the necessity, as in the manufacture of crystalline low-retentivity metal alloys (which have been standard up to now in the art), to carry out a multitude of rolling and/or forming steps, with numerous intermediate annealings.
For various applications, for example, in chokes, cores with sheared hysteresis loops are often employed. As is known, one can achieve a shearing in cores comprised of standard crystalline low-retentivity alloys by providing an air gap at least at one location along the core body, which air gap then extends over the entire core cross-section at such location.
Such air gaps must often be produced in a relatively expensive manner or the cores must be completely cut-through at select locations in order to create the air gap, as is the case, for example, in cut tape cores so that additional elements for holding the core together, for example, tightening straps and the like, are required.